Bacillary angiomatosis (BA) is a vascular proliferative disease of the skin and visceral organs initially described in HIV-infected patients. The etiologic agents of this disease are two species of highly fastidious, and closely related bacteria, Rochalimaea henselae and R. quintana. Since BA is a newly described disease and R. henselae is a recently described organism, the important, immunologically active antigens of these organisms have not yet been defined. The long range goals of the proposed studies are to identify immunologically active proteins of R. henselae and R. quintana and to characterize their roles in the immune response to Rochalimaea infection. These studies are designed to produce new information about the antigenic composition of Rochalimaea and the humoral immune response to infection with Rochalimaea. By analyzing specific Rochalimaea antigens (and their genes) at the molecular level, we should be able to produce valuable reagents for the diagnosis of Rochalimaea infections. Specific aims of the project are: 1) identify the immuno-dominant antigens of R. henselae and R. quintana; 2) cloning and sequencing the genes coding these major antigenic proteins; and 3) evaluating the recombinant antigens as diagnostic reagents for BA and cat-scratch disease (CSD). The basic approach will be to screen recombinant gene libraries of R. henselae and R. quintana for expression of antigens reactive with human sera from patients with BA and GSD. Immunoreactive clones will be subcloned, and sequenced and these recombinants will be sources of individual proteins for evaluation as immunodiagnostic reagents and studies to analyze their roles in the immune response to infection with Rochalimaea.